This past season, Doctor Who fans have been repeatedly teased about the “Hybrid,” a destructive figure of myth who strikes fear in members of many races and yet has never been mentioned until now. It happens. Several suspects have been brought up across the episodes, including the Doctor himself. The Hybrid is supposed to be the product of “two warrior races” and the Doctor is certainly one who’s been shaped by his experiences and anger towards both the Daleks of Skaro and the Time Lords of Gallifrey. But in the season 9 finale “Hell Bent,” a character suggested the hero may be a literal hybrid, one who repeatedly looks after Earth because one of his parents is actually a human being. So is the Doctor half human?

During the classic series, this was never a question. Certain writers and showrunners debated why the Doctor left his planet Gallifrey (creator Sydney Newman thought he was escaping a war whereas producer/showrunner Verity Lambert liked to think he was a criminal escaping punishment), but there was never any debate about whether he was full alien or not. The idea first came up in the 1996 Doctor Who TV-movie. The villain known as the Master examines the Doctor’s new, eighth incarnation and notices that he has a human retinal pattern. He then remarks, “The Doctor is half human.” Later in the movie, the Eighth Doctor seemingly confirms the Master’s suspicions, remarking to a person he’s trying to distract, “I’m half human. On my mother’s side.”

The TV-movie was a joint venture between BBC Worldwide, Universal Studios and 20th Century Fox. The original idea was that this movie would be a reboot of the Whoniverse rather than continue the established saga of the classic TV series that aired from 1963-1989, featuring seven incarnations of the Doctor. During the early stages of planning, it was decided that the Doctor adventuring at random for enjoyment and curiosity’s sake wasn’t a strong idea, that it would be better if he were on a specific quest and just happened to have adventures along the way. It was also believed that there needed to be a concrete reason why he protected Earth so often beyond simply saying he liked humans and that the planet tended to get in trouble more often than a lot of others.

So two things were proposed. One, that the Doctor left Gallifrey to find his father, a Time Lord named Ulysses who had vanished long ago and visited Earth several times (at one point living there as Blackbeard the Pirate). The second idea was that the Doctor’s mother would turn out to be a human native to Earth (which was also going to account for the Doctor having blue eyes, a trait apparently bizarre by Gallifreyan standards). Later in production, it was decided to alter the story of the TV-movie and keep it largely in line with the continuity of the classic TV program, but obviously the half-human idea still made it to screen.

For some fans, this idea was immediately accepted as canon. It made sense to them, seemed no stranger than the fact that the Doctor traveled through space and time in a box that defied physics, and gave a new mystery to explore concerning his heritage and upbringing. For instance, if he did have a human mother, who had she been and just when the Doctor discover this? Had they ever met?

Many other fans dismissed the idea though, arguing that the Time Lords (including the Master) would have known and remarked on the Doctor’s mixed heritage long ago if it were easily discovered by simply looking at his eyes and that this story point unnecessarily gave the Doctor reasons behind his behavior when it had been accepted for decades that he simply had a fondness for Earth people (even if they ticked him off just as often).

What about the Doctor’s remark that his mother was human? Well, the critics said, this was said while he was trying to distract the guy from realizing that the Doctor was picking his pocket, so why take a distraction technique that seriously? But what about what the Master saying the Doctor’s eyes were human? Well, the Master was, at that time, forcibly inhabiting a human corpse that was slowly decaying and that, along with his increasing insanity, means that what he thought he saw can’t be trusted. Perhaps the Doctor’s joke was just a coincidence.

During an interview on the podcast Toby Hadoke’s Who’s Round, former Doctor Who showrunner Russell T. Davies (who spearheaded the program’s revival in 2005) remarked that he had deliberately not addressed the half human idea, but also felt it couldn’t be totally ignored. He said, “I don’t like the half human thing. He certainly isn’t half human, but it’s less interesting to say it simply doesn’t count. I always wanted to put in a line where someone says to the Doctor, ‘Are you human?’ And the Doctor says, ‘No, but I was once in 1999. It was a 24-hour bunk.’ Part of the reason I never put that in was it was a bit too self-referential but also I thought, ‘I’m spoiling the TV-movie if I do that.'”

In keeping with his idea that the Doctor was not half human, Russell T. Davies introduced a clone of the Doctor, the “Meta-Crisis Doctor,” who was surprised to realize he was half-human due to the circumstances of his creation. In his final episode as showrunner, Davies also introduced a Time Lord woman from Gallifrey whom he considered to be the Doctor’s mother. However, he deliberately did not have this explained on screen and only referred to her as “The Woman” in the script, so as not to set the Doctor’s parentage in stone and prevent future storytellers from exploring different ideas.

When BBC Books released its Eighth Doctor Adventures (EDA) novel range, the half human idea was addressed a couple of times. In The Scarlet Empress, the Doctor remarks that he once mistakenly thought he had a human mother (making a joke about such a thing certainly wouldn’t be the oddest thing he’s said or done hours after a regeneration). In Autumn Mist, he joked that his heritage was “debatable.” In the seventy-third and final EDA novel, The Gallifrey Chronicles, it is revealed that a Time Lord named Ulysses had a son with a human named Penelope Gate, a woman from the 19th century who had appeared once previously in the Seventh Doctor novel The Room with No Doors. Though the novel didn’t actually say who this half human son was or grew up to be, some fans decided this settled the debate and it was, indeed, the Doctor. Others felt fine with ignoring this conclusion, as it had not been established anywhere that Ulysses was the name of the Doctor’s father, that had just been an idea that never made it to screen.

There’s also been the thought that while the Doctor is not half human, his eighth incarnation was. In the novel Human Nature and its TV adaptation episodes (“Human Nature” and “The Family of Blood”), the Doctor uses Time Lord technology to alter his biology to that of a human being. The comic book mini-series The Forgotten had the Eighth Doctor remark that he had used the same technology during the Doctor Who TV-movie to trick the Master into thinking he was half human, though when he actually achieved this transformation and what advantage it gave him was never detailed.

Along with this, the Time Lord Romana indicated in the TV story “Destiny of the Daleks” that Time Lords could regenerate into seemingly non-Gallifreyan, non-human looking forms (in her case, she considered becoming a blue-skinned humanoid). This, along with the Doctor’s remark in the TV-movie that he could “change species” when he was dying had some conclude that only the eighth incarnation was half human, perhaps as a side effect of what we saw was a very difficult regeneration. Other regenerations are near-instantaneous or take a few minutes, but the TV-movie showed a three-hour gap between the Doctor’s seventh body dying and his transformation into his eighth self, and even then he was largely amnesiac. The Eighth Doctor said that anesthetic drugs that had been forced into his body had “almost destroyed the regenerative process.” The change was possibly also more difficult this time due to it being the only regeneration we’ve seen on-screen where neither Gallifreyan technology nor other Time Lords were present. Perhaps these factors led to a biological alteration that remained with him until he regenerated again into the War Doctor (thus, losing some humanity physically and not just symbolically). The War Doctor himself was born out of manipulation by the Sisterhood of Karn, who were originally Gallifreyans (an idea proposed in the novels and accepted and repeated on the official BBC web-site) and who had chemicals and “magic” that was known to control regeneration (as first revealed in “The Brain of Morbius”).

I recently chatted on this subject with Will Brooks (@WillBrooks1989), a designer who has done quite a lot of Doctor Who work, including recent covers for Titan’s DW comics, as well as art for Big Finish Productions and BBC Worldwide. Will proposed that the Doctor’s weakened and slow regeneration, happening in a morgue, was influenced by the DNA of the surrounding corpses—hence a half human eighth incarnation. This idea of the change influenced by surrounding life forms has definitely been seen elsewhere in Doctor Who. In the Big Finish audio drama Circular Time, a Time Lord regenerates into an incarnation who is a hybrid, combining Gallifreyan DNA with that of the dominant life form of the planet he chose to live on.

My own idea for some time is in line with the belief of some fans that the Doctor’s last thoughts during regeneration will influence how the next incarnation will be. The Seventh Doctor was also known as the “master planner” and the “schemer.” He was more manipulative than many of his other incarnations and much more proactive in hunting evil and setting it up to destroy itself, leading to decisions he was not proud of and would lament in his private moments. In the audio play The Clockwork Men, the Doctor called his seventh self “obsessed with the future” and the “big picture,” adding: “The more he planned, the more he gained, the more he realized he was losing the one thing most precious to him… He only wanted to be more human.”

In his final moments, I like to think the Seventh Doctor told himself, “I became too much of a Time Lord again, too concerned with the math and the big picture rather than the individual. I hope next time I’m more human.” And regeneration granted his wish.

Is the Doctor half human? Short answer: maybe. I don’t personally think he needs to be and I like to keep his origins a mystery so that you can still rightfully call the series Doctor Who, but I also wouldn’t mind it if it brought along a new story that entertains and inspires discussion. In the Whoniverse, anything and everything is possible.

Alan Kistler (@SizzlerKistler) is the author of the New York Times Best Seller Doctor Who: A History. He is freelance writer, actor, story consultant and pop culture historian focusing on science fiction and American superheroes. Tom Baker and Paul McGann are his Doctors.